The present invention relates to apparatus for measuring the percentage of dissolved gas in a liquid, in general, and to relatively compact apparatus for rapidly measuring dissolved gas percentages in liquids moving within a conduit or similar enclosure, in particular.
The presence of dissolved gas in a liquid can produce any number of unwanted conditions in various manufacturing industries. In, for example, the photographic industry, the presence of dissolved gas in a coating fluid can have a decidedly negative impact on a finished photographic product. During the process of coating photographic films, for example, coating fluids are often subjected to pressures well in excess of and well below atmospheric pressure. If the coating fluid contains a significant amount of dissolved gas and this dissolved gas containing liquid is subjected to a low enough negative pressure, the dissolved gas will come out of solution in the form of gas bubbles. Gas bubbles in a photographic film coating fluid creates voids in the coating fluid that shows up as spots or imperfections in a finished photographic print. If the presence of dissolved gas in a photographic film coating fluid can be timely determined, steps can be taken to either remove any resulting gas bubbles or to preferably prevent the occurence of such gas bubbles by subjecting the dissolved gas containing coating fluid to conventional degassing techniques.
Several different techniques are presently available for measuring the percentage of dissolved gas in a liquid. However, each of these techniques suffers from one or more shortcomings that render them either unsuitable, inadequate or less than desirable for the dissolved gas measurement task presented.
In many applications it is desirable to have the percentage of dissolved gas rapidly and continuously measured. However, some gas measurement techniques involve the time-consuming task of extracting a sample of the liquid to be tested and then transporting same to a laboratory where the amount of dissolved gas is determined by observing bubble formation in the liquid while the liquid is being subjected to negative and positive pressures. Other techniques either employ apparatus that is not compatible with the liquid to be tested in that it might introduce contaminants into the liquid or are not capable of measuring the type of gas that is dissolved in same. Still other techniques determine dissolved gas percentage by changing the basic character of the liquid such as by burning or oxidizing same. In order to prevent contamination, the liquid sampled in such instances is precluded from being returned to the main body of liquid after dissolved gas measurements have been completed. This technique can produce a significant waste of liquid if employed over an extended period of time.
In U.S. Pat. No. 3,871,228 to WEISS, apparatus is disclosed for measuring the total pressure of gas components present in a large body of water. The apparatus includes a hollow tube-shaped gas permeable member for immersion in said body of water that is coupled to a pressure sensor having the form of either a manometer or a low internal volume pressure gauge. In addition to the excessive quantity of tubing-shaped membrane, employed, which would make such an arrangement unsuitable for the measurement of a process liquid moving within a relatively small conduit, the combined internal volume of the tubing, pressure gauge and coupling means between same is excessive for rapid pressure measurement and if such apparatus is employed to measure the total pressure of gas components in a liquid that is warmer than said apparatus, liquid vapor permeating the membrane will condense into a liquid within said membrane, thereby precluding meaningful measurement of gas pressures within said warmer liquid.
The primary object of the present invention is, therefore, to provide apparatus for rapidly and continuously measuring the percentage of dissolved gas in a liquid moving within a conduit.
Another object of the present invention is to provide apparatus for measuring the percentage of dissolved gas in a liquid whose temperature is higher than that of the dissolved gas measuring apparatus.
A further object of the present invention is to provide apparatus for measuring the percentage of dissolved gas in a liquid that is relatively compact and chemically compatible with the liquid to be measured.
Other objects, features and advantages of the present invention will be readily apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.